1. Field of the Invention
This invention relates to tamperproof packaging and, more specifically, it relates to a tamper evident package and composite material and a method of sealing packages such that a clear indication would be given if any tampering occurs and more specifically the invention relates to a tamper evident composite material useful as an exterior packaging material and as a non-transferable label or sticker which has a layer of material that becomes extremely brittle once cured. A package sealed with this packaging material cannot be unsealed without noticeably shattering the packaging material.
2. Description of the Prior Art
The tampering with and adulteration of many commercially available products has become a critical problem endangering health and sanitation. Many products which are adulterated or tampered with ultimately reach a consumer bearing no indication that such adulteration or tampering has occurred. Accordingly, it is highly desirable to provide a type of packaging material which would give an indication that there has been interference with the integrity of the product packaging.
Various mechanical indications used to determine the integrity of several types of products and containers have been known. For example, U.S. Pat. No. 3,662,915 relates to a tamperproof package which provides a recessed tab in the inner periphery of a container which breaks away from the remainder of the container when entry is made into the container so as to indicate that tampering with the package has occurred.
It has known to employ elastomeric materials disposed in protective surrounding relationship with respect to a container. See U.S. Pat. Nos. 4,546,881, 4,449,632, and 4,181,223.
U.S. Pat. No. 2,074,490 discloses a tamperproof container in the form of a tinplate container having a composite coating consisting of a heat sensitive paint, printing ink, and varnish. This coating is said to distort responsive to any effort to remove the can end, get access to the contents, and then solder the end to the can.
It has been known to provide for rupturing of outer coatings which fracture responsive to operation of a tear strip. See U.S. Pat. No. 3,415,402. See also U.S. Pat. No. 4,479,585.
It has been known to protect printed circuit boards by ultraviolet curable polymeric coatings which are intimately bonded to such boards. See U.S. Pat. Nos. 4,451,523 and 4,424,252.
In addition to such mechanical indicators, it has been known to provide a color indication that package integrity has been interrupted. For example, U.S. Pat. No. 3,935,960 provides a hermetically sealed container having a tape closure over an aperture for removing the contents of the container. The tape closure is provided with an indicator layer of color capsules which rupture when the tape closure is removed.
U.S. Pat. No. 4,502,605 provides an indicator dye/activator system which is mounted on the cap of a container in such a way that opening the cap of the container causes the indicator material to oxidize and thereby change in color. It teaches the use of a volatile alkali solution such as ammonia as an activator having a pH in the range of 9-12 whereas atmospheric and has a pH in the range of 5-7. The preferred indicator dye is sold to be phenolphthalein or other dyes sensitive to changes in the pH. See also U.S. Pat. No. 4,516,679.
U.S. Pat. No. 4,098,577 also discloses use of a pH sensitive dye which will display a different color when in contact with atmospheric air which would occur when the package is opened. U.S. Pat. No. 4,505,399 provides a sheet of material sensitive to light or oxygen which would effect a time-delayed, irreversible change in appearance in response to exposure. The sensitive material would be placed between two inactive sheets and the combination would be placed over the opening to the container so that the sensitive sheet would have to be exposed when the container is opened.
Some of the problems which have been encountered in using the prior art techniques are that they can be circumvented by various means. In addition, the known methods are primarily confined to use with certain types and configurations of containers.
U.S. Pat. No. 4,890,763 discloses the use of an exterior coating which is extremely brittle and which will shatter when any puncture of the coating occurs. Even though it is capable of providing an effective method to indicate that a product has been tampered with or adulterated, the utilization of this coating is extremely difficult. The liquid coating, when applied to an object, is capable of leaking through gaps at the seams of the container or gaps in the closure of the container opening into the container, resulting in contamination of the materials in the container. In addition, the flow of the liquid coating is influenced by gravity, wetting forces and various other factors. Thus the resulting coatings after curing often exhibit irregular shapes with great variations in thickness making the coating very unattractive to the consumers and difficult to package because of the irregularity in size.
In spite of the existing prior art techniques, there remains a need for an effective method of indicating that a product has been tampered with or adulterated. There remains a need for such a method which is economical and easy to use with a wide range of package configurations without risk of contamination.